1. Field of the Invention
The invention is directed to the field of manufacturing electronic devices. More specifically, the invention is directed to methods and apparatus used to increase yield during fabrication of electronic devices.
2. Description of Related Art
In order to increase the yield (i.e., the ratio of good devices to the total number of devices available) during the manufacture of electronic devices such as semiconductor integrated circuits, redundant blocks or sections (e.g., memory elements) which are substantially similar in function and/or structure to components on the electronic device are incorporated into the manufactured device. These redundant blocks can be substituted for defective blocks to salvage an otherwise inoperable device. The substitution of these redundant blocks, however, requires overhead circuitry used to test and substitute the redundant blocks. As integrated circuits become more dense, such added circuitry required to access the redundant blocks becomes excessive.
An alternative to the use of such redundant circuitry is known as "discretionary wiring." According to this concept, a semiconductor wafer 10 (FIG. 1) contains small, similar semiconductor devices or clusters of devices 12 which are manufactured using traditional batch processing methods. Before these clusters are interconnected, however, they are tested and a map of good and bad elements 12 on the wafer 10 is created. For each wafer 10, a set of unique masks for the interconnect patterns (i.e., "discretionary wiring") is created and metallic conductive strips 18 (FIG. 2) are fabricated on the wafer 10 to interconnect all the good elements 12 into a single functional integrated circuit.
A process that employs discretionary wiring by preparing unique masks for the interconnect layer of the semiconductor device is shown in U.S. Pat. Nos. 3,771,217 and 5,691,949. Preparing a unique interconnect pattern using a separate masking step can be a costly and time intensive operation.